More than 50 people were injured in the attack

Authorities had initially said that they were investigating the connection, but national police chief Leandro Mendoza said at a news conference in Manila on Thursday that he had since ruled out any ties with al-Qaeda.

He said that the two suspects, Rodel Ladrera and Marvin Geonzon, were believed to be members of the Abu Sayyaf rebel group.

The police did not give any details of a third suspect, who is still being held in Zamboanga.

Military offensive

The Abu Sayyaf is fighting for a Muslim homeland in the southern islands of the Philippines. It has carried out a campaign of kidnappings and is thought to be holding an American couple and about 10 Filipinos hostage.

US military are advising the Philippines government

The Philippine military has been conducting a fierce offensive against the rebels on the main southern island of Mindanao and two smaller islands of Basilan and Jolo.

In the latest series of clashes, the Filipino authorities said on Thursday at least nine Abu Sayyaf gunmen had been killed in two separate incidents on Basilan.

A team of 23 US military advisers is expected to meet top military officials in the capital of the Philippines, Manila.

They have spent the last week in the southern Philippines assessing the needs of the armed forces in their efforts to rescue the Abu Sayyaf's hostages.

A Filipino spokesman said the team had identified problems with insufficient resources relating to mobility like inter-island vessels, cargo planes, helicopters and lorries.